[llvm] [llvm] Win x64 Unwind V2 1/n: Mark beginning and end of epilogs (PR #110024)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

Overall, this seems fine, but I'd like to see some description of the binary layout before we start landing patches.

https://github.com/llvm/llvm-project/pull/110024